This invention relates to a crawler vehicle and a data processing system wherein the crawler crawls along the floor of a tank containing a liquid for inspection of the integrity of the floor of the tank and, more particularly, to the provision of the crawler with coarse and fine data gathering capability suitable for a precise mapping of a tank floor.
Tank farms have numerous tanks situated above ground for holding various types of liquid ranging from volatile combustible hydrocarbons, such as gasoline or other explosive material, to non-hazardous liquid substances such as water-based food products. With the passage of time, the floor of the tank may corrode from the inside and/or the outside, and exhibit pitting and cracking. Such forms of corrosion introduce a weakness to the floor of the tank with the possibility of a leak in the tank. To insure the integrity of the tank, it is the practice to conduct periodic inspections of the tank so as to detect signs of wear well before a failure occurs, and also to predict a rate of degradation of the tank floor for assessing an appropriate schedule for periodic inspection.
A problem arises in that tank inspection procedures are often accomplished by taking the tank out of service, opening up a passage in a sidewall of the tank, venting the tank of all possible hazardous vapors, and then allowing personnel to enter the tank for conducting the inspection. Typically, in the conduct of the inspection, it is the practice to clean sediment from the floor of the tank, thereby to expose numerous portions of the floor whereupon electromagnetic or acoustic sounding devices can be employed for supplementing visual observation of the floor by determining the thickness of the floor and anomalies due to pitting and cracking.
It is recognized that, in the case of periodic inspection, it is desirable to reinspect the same locations which have been inspected previously, thereby to enable a comparison of conditions over a number of inspections for determining a rate of degradation. This requires some form of mapping procedure to insure that the same areas are being inspected each time. Thus, there is a further problem in that there is a need for precise mapping apparatus which is not presently available. In the case of inspection of tanks containing fossil fuels, such as petroleum, the venting of the noxious fumes as well as other procedures of the inspection are carried out in accordance with API 653 recommended practice for maintenance.